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# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
from typing import TYPE_CHECKING, Union
from astroid import nodes
from pylint import checkers, interfaces
from pylint.checkers import utils
if TYPE_CHECKING:
from pylint.lint import PyLinter
_LIST_MODIFIER_METHODS = {"append", "remove"}
_SET_MODIFIER_METHODS = {"add", "remove"}
class ModifiedIterationChecker(checkers.BaseChecker):
"""Checks for modified iterators in for loops iterations.
Currently supports `for` loops for Sets, Dictionaries and Lists.
"""
__implements__ = interfaces.IAstroidChecker
name = "modified_iteration"
msgs = {
"W4701": (
"Iterated list '%s' is being modified inside for loop body, consider iterating through a copy of it "
"instead.",
"modified-iterating-list",
"Emitted when items are added or removed to a list being iterated through. "
"Doing so can result in unexpected behaviour, that is why it is preferred to use a copy of the list.",
),
"E4702": (
"Iterated dict '%s' is being modified inside for loop body, iterate through a copy of it instead.",
"modified-iterating-dict",
"Emitted when items are added or removed to a dict being iterated through. "
"Doing so raises a RuntimeError.",
),
"E4703": (
"Iterated set '%s' is being modified inside for loop body, iterate through a copy of it instead.",
"modified-iterating-set",
"Emitted when items are added or removed to a set being iterated through. "
"Doing so raises a RuntimeError.",
),
}
options = ()
priority = -2
@utils.check_messages(
"modified-iterating-list", "modified-iterating-dict", "modified-iterating-set"
)
def visit_for(self, node: nodes.For) -> None:
iter_obj = node.iter
for body_node in node.body:
self._modified_iterating_check_on_node_and_children(body_node, iter_obj)
def _modified_iterating_check_on_node_and_children(
self, body_node: nodes.NodeNG, iter_obj: nodes.NodeNG
) -> None:
"""See if node or any of its children raises modified iterating messages."""
self._modified_iterating_check(body_node, iter_obj)
for child in body_node.get_children():
self._modified_iterating_check_on_node_and_children(child, iter_obj)
def _modified_iterating_check(
self, node: nodes.NodeNG, iter_obj: nodes.NodeNG
) -> None:
msg_id = None
if self._modified_iterating_list_cond(node, iter_obj):
msg_id = "modified-iterating-list"
elif self._modified_iterating_dict_cond(node, iter_obj):
msg_id = "modified-iterating-dict"
elif self._modified_iterating_set_cond(node, iter_obj):
msg_id = "modified-iterating-set"
if msg_id:
self.add_message(
msg_id,
node=node,
args=(iter_obj.name,),
confidence=interfaces.INFERENCE,
)
@staticmethod
def _is_node_expr_that_calls_attribute_name(node: nodes.NodeNG) -> bool:
return (
isinstance(node, nodes.Expr)
and isinstance(node.value, nodes.Call)
and isinstance(node.value.func, nodes.Attribute)
and isinstance(node.value.func.expr, nodes.Name)
)
@staticmethod
def _common_cond_list_set(
node: nodes.Expr,
iter_obj: nodes.NodeNG,
infer_val: Union[nodes.List, nodes.Set],
) -> bool:
return (infer_val == utils.safe_infer(iter_obj)) and (
node.value.func.expr.name == iter_obj.name
)
@staticmethod
def _is_node_assigns_subscript_name(node: nodes.NodeNG) -> bool:
return isinstance(node, nodes.Assign) and (
isinstance(node.targets[0], nodes.Subscript)
and (isinstance(node.targets[0].value, nodes.Name))
)
def _modified_iterating_list_cond(
self, node: nodes.NodeNG, iter_obj: nodes.NodeNG
) -> bool:
if not self._is_node_expr_that_calls_attribute_name(node):
return False
infer_val = utils.safe_infer(node.value.func.expr)
if not isinstance(infer_val, nodes.List):
return False
return (
self._common_cond_list_set(node, iter_obj, infer_val)
and node.value.func.attrname in _LIST_MODIFIER_METHODS
)
def _modified_iterating_dict_cond(
self, node: nodes.NodeNG, iter_obj: nodes.NodeNG
) -> bool:
if not self._is_node_assigns_subscript_name(node):
return False
infer_val = utils.safe_infer(node.targets[0].value)
if not isinstance(infer_val, nodes.Dict):
return False
if infer_val != utils.safe_infer(iter_obj):
return False
return node.targets[0].value.name == iter_obj.name
def _modified_iterating_set_cond(
self, node: nodes.NodeNG, iter_obj: nodes.NodeNG
) -> bool:
if not self._is_node_expr_that_calls_attribute_name(node):
return False
infer_val = utils.safe_infer(node.value.func.expr)
if not isinstance(infer_val, nodes.Set):
return False
return (
self._common_cond_list_set(node, iter_obj, infer_val)
and node.value.func.attrname in _SET_MODIFIER_METHODS
)
def register(linter: "PyLinter") -> None:
linter.register_checker(ModifiedIterationChecker(linter))
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